If you're thinking about goals for 2013, one of them should definitely be to learn a new art form. Why? SO MANY REASONS.
First of all, learning is good for your brain. It doesn't really matter what you are learning; it makes new neural pathways in your brain, improves your brain's plasticity, and helps you make more connections in other aspects of your thinking. Learning is just plain good for you, which is why it's such a shame that most of us essentially stop learning once we leave school.
Learning a new art form will improve your current art. Let's say that you are a watercolor painter. If you take a ceramics class, or learn woodworking, or glassblowing, you will soon notice an improvement in your watercolors. Learning a new art form gives you a new perspective on your current art. Nothing makes you appreciate your experience in one field like becoming a rank amateur in a new field.
Techniques can be surprisingly transferrable. For example, working with ceramics can help improve your fine motor skills, which is certainly a benefit to painters. It also gives you a new outlook on volume and shape, which can bring more life to your watercolors. By contrast, a ceramics artist who takes a painting class might come away with a new appreciation for light/dark contrast and color theory.
You might really enjoy it! What if our hypothetical watercolor artist discovers that inside her is a ceramics artist who has been yearning for freedom her entire life. Whatever age you are, it's never too late to discover a new passion. Maybe oil painting or weaving or metalworking is your true calling - but you will never know unless you give it a try.
It will broaden your understanding of the arts. When you learn about ceramics (for example), you also learn about the history of ceramics. You learn about the popular styles, historical glazes, and various cultural aesthetics. Each art form has its own huge volume of art history. The more you know about one, the more you know about all.
It will humble you. We all love to be the big fish in the small pond. If you have been painting for 20 years, it's easy to get complacent. And when you get complacent, your art suffers. There's no better way to knock yourself out of that rut than to try something new, and have that experience of being a newbie all over again.